Inorganic compounds and materials as catalysts for oxidations with aqueous hydrogen peroxide

This paper reviews our work on oxidations with aqueous hydrogen peroxide catalyzed by inorganic catalysts devoid of organic ligands. In the first part of the review, the use of the [WZn₃(ZnW₉O₃₄)₂] ^12- "sandwich" polyoxometalate as a multi-purpose oxidation catalyst is described. Attention is paid to practical aspects that are of relevance for large-scale, industrial use of this catalyst, such as catalyst preparation, handling, and recycling. Its activity in cyclooctene epoxidation compared to other W-based catalyst systems has been determined under ceteris paribus conditions. The second part of the review deals with homogeneous and heterogeneous inorganic catalysts for "dark" singlet oxygenation, i.e., singlet oxygenation by catalytic disproportionation of hydrogen peroxide into singlet oxygen and water. The industrial advantages of "dark" singlet oxygenation compared to conventional photo-oxidation are described. It is pointed out that the reaction medium and nature of the catalyst strongly influence the selectivity and scope of the method.